Biomarkers are molecular indicators of a specific biological property, a biochemical feature or facet that can be used to measure the progress of disease or the effects of treatment.
Proteins and nucleic acids are exemplary biomarkers. In particular, it has been widely accepted that genomic messengers detected extracellularly can serve as biomarkers for diseases [6]. In particular, nucleic acids have been identified in most bodily fluids including blood, urine and cerebrospinal fluid, and have been successfully adopted for using as diagnostic biomarkers for diseases [28, 42, 49].
Saliva is not a passive “ultrafiltrate” of serum [41], but contains a distinctive composition of enzymes, hormones, antibodies, and other molecules. In the past 10 years, the use of saliva as a diagnostic fluid has been successfully applied in diagnostics and predicting populations at risk for a variety of conditions [47].
Specific and informative biomarkers in saliva are desirable to serve for diagnosing disease and monitoring human health [30, 47, 6]. For example biomarkers have been identified in saliva for monitoring caries, periodontitis, oral cancer, salivary gland diseases, and systemic disorders, e.g., hepatitis and HIV [35]. Also previous studies show that human DNA biomarkers can be identified in saliva and used for oral cancer detection [30, 36]. RNA is more labile than DNA and is presumed to be highly susceptible to degradation by RNases. Furthermore, RNase activity, is reported to be elevated in saliva, which constitutes an inexpensive, non-invasive and accessible bodily fluid suitable to act as an ideal diagnostic medium. In particular, RNAase activity is reported to be elevated in saliva of cancer patients [83]. It has, thus, been commonly presumed that human mRNA could not survive extracellularly in saliva. OSCC is the sixth most common cancer in the world, and affects 50,000 Americans annually. Worldwide, cancers of the oral cavity and oropharynx represent a great public health problem. OSCC accounts for nearly 50% of all newly diagnosed cancers in India and is a leading cause of death in France [1].
Despite improvements in locoregional control, morbidity and mortality rates have improved little in the past 30 years [2]. Therefore, early detection or prevention of this disease is likely to be most effective. Detecting OSCC at an early stage is believed to be the most effective means to reduce death and disfigurement from this disease. The absence of definite early warning signs for most head and neck cancers suggests that sensitive and specific biomarkers are likely to be important in screening high risk patients.